In the oil and gas industry, and in other related industries, salt dome caverns within the earth are utilized for storing liquid or gaseous materials such as oil, natural gas, butane, hazardous waste and the like. These salt dome caverns are accessed first by drilling a well from the surface into the salt dome, lining the drilled well borehole with casing, and then removing the undesired salt from the salt dome with fresh water to create the desired storage area. Many different techniques are used to remove the salt and create the storage area, the most common of which is fresh water etching or in situ salt mining.
After the cavern has been etched to the desired storage capacity, the well may be utilized for product storage. It is present industry practice to place tubing down into the cavern storage area through the cased borehole. The tubing is suspended in the cased borehole by a casing hanger. A wellhead casing with inlet and outlet flanges, fitted with appropriate valves, are connected to both the tubing and borehole casing. The tubing and the cased borehole serve dual purposes as both may be used as a conduit to and from the cavern storage area for placing and for removing the stored product through their respective inlet and outlet flanges.
Once created the cavern storage area typically contains brine water which is a by product of the cavern formation process. In storing product the brine water is displaced by the product as it is injected into the cavern. In removal of product, brine water is injected for displacing the stored product out of the cavern storage area.
To store a gas product such as butane gas in the cavern, it is current practice to place the gas into the underground cavern storage area by injecting the gas into the cased borehole through the wellhead casing inlet and casing flange down into the cavern. This gas displaces the stored brine water and effectuates its flow upward through the tubing to the surface through the tubing outlet flange in the wellhead for storage or disposal.
Product is removed in a similar manner, that is, by injecting brine water through the wellhead tubing inlet and tubing inlet flange down into the cavern to displace the stored gas and effectuate its flow upward to the surface for exit through the cased borehole outlet flange. The stored gas may then be transported for use. The flow of the displacing gas or brine water into and out of the storage cavern is typically controlled at the surface by a system of piping and surface control valves connected to the wellhead inlet and outlet flanges.
This current practice of only utilizing surface controls for the flow into and out of the storage well leaves the storage well and the stored product vulnerable to the atmosphere and at risk to explosion or blowout in the event of a disruption of the surface control valve system. While subsurface control valves are utilized in the oil and gas industry for control of producing wells, such valves are not utilized and are not readily adaptable for utilization on salt dome storage wells. At present, no system exists to provide a subsurface control valve that will accommodate the current techniques utilized to remove product from the storage caverns.
For instance, in production wells the annulus area (the area between the casing and the tubing) is typically sealed by a packer situated above the production zones of the well. The packer seal diverts the production flow from the annulus to the production tubing which is used to bring the production to the surface. Tubing chokes such as those illustrated in U.S. Pat. Nos. 2,785,755, 2,796,133 and 2,831,539 all to En Dean for oil well storm chokes are then utilized to shut off production in the tubing in the event of a catastrophic situation. The storm choke and packer combinations are not used to control annular flow of the product as in the case of salt cavern storage wells.
Other subsurface control valves are illustrated in U.S. Pat. No. 3,079,923 to Tausch, U.S. Pat. No. 3,457,991 to Sizer, et al and U.S. Patent Reissue No. 25,109 to Natho.
The Natho and Tausch patents teach methods for shutting off the flow in production tubing. Flow in the annulus is controlled by conventional packers as in the En Dean patents. The Sizer, et al patent teaches a production tubing control valve device where annular flow is shut off by means of conventional blowout preventers. These devices do not teach a technique for opening and closing an annular spaced utilized for product flow as in a salt dome storage facility.
Devices or means for control of pressurized storage facilities such as salt dome caverns are disclosed in U.S. Pat Nos. 3,530,674 to Cobbs, et al, 3,105,358 and 2,901,889 to Reed and 4,842,074 to Hines, et al.
The Cobbs patent discloses a method of controlling the pressure in the cavern storing anhydrous ammonia with a column of water in the annular space. The U.S. Pat. No. 3,105,358 Reed patent is directed toward sealing the annular by means of a spring biased check valve as a means to remove subsurface pumps. It does not afford a downhole shutout mechanism in the event of a catastrophe at the surface as the disclosed device requires manual removal of the surface valve bushing and repositioning of the valve flanges to shut off annular flow.
The U.S. Pat. No. 2,901,889 Reed patent teaches pressurizing the dome cavity. The U.S. Pat. No. 4,842,074 Hines, et al patent incorporates a downhole packer for directing the fluids or gas downhole by means of pressure generated at the surface level through surface control valves. Neither provides or discloses a means for subsurface shut off of product flow in the event of a catastrophic event at the surface of a storage well.
Consequently, a need exists for improvements in subsurface control of flow from underground salt dome storage wells which will allow the conventional techniques of storage and removal to be utilized but at the same time provide a means to shut off flow in the event of a surface catastrophe.